The need to define the events of tumor-host interactions in modern immunological terms is apparent. By using autochthonous or transplanted syngeneic tumors in mice (including spontaneous mammary tumors and chemically induced lung adenocarcinomas) we will attempt to define: the dynamics of development of immunity after immunization; the dynamics of development of concomitant immunity in the tumor bearing host, the cell types involved in the response and regulation of such response especially T-dependent ones; the antibodies produced during such responses and the significance of the different tumor-associated antigens in triggering "selectively" humoral or cellular immunity and amplifying or suppressive mechanisms. The mammary tumor in mice has some intrinsic advantages for the study of such events since some of the viral antigens are relatively well defined biochemical entities.